Updated: May 2
This article acts as a followup to our first article on the Jehovah's Witnesses which expanded into JW proof texts in which they attempt to show that Christ is not God in the flesh.
This article will expand more into other problems the Jehovah's Witnesses face that may not even be known by them. Combining this article with the first article (which preferably must first be read here) it should act as a solid defence of the Gospel and exposure of the inherent problems within JW beliefs.
In the following post, red text indicates official Watchtower content or statements.
Always keep in mind to make the Gospel a central part of your conversation with the JW. If you destroy their worldview but you don't bring them the Gospel, you've accomplished absolutely nothing.
Who/what is the authority of the JW?
Ask the JW who their authority is. They might answer one of two things:
The Watchtower and Bible Tract Society forbids the reading of outside literature, and claims that studying the Bible alone leads to apostasy, yet its false prophecies destroy its claim to sole authority and truth. Therefore being a JW you cannot consistently hold to either!
Not only do we find that people cannot see the divine plan in studying the Bible by itself, but we see, also, that if anyone lays the “Scripture Studies” (his books) aside, even after he has used them, after he has become familiar with them, after he has read them for ten years – if he then lays them aside and ignores them and goes to the Bible alone, though he has understood his Bible for ten years, our experience shows that within two years he goes into darkness. On the other hand, if he had merely read the “Scripture Studies” with their references and had not read a page of the Bible as such, he would be in the light at the end of two years, because he would have the light of the scriptures.
Watchtower, Sep. 15, 1910, p. 298
If the JW's authority is Scripture, it's inconsistent with JW doctrine. If it's the Watchtower, their false prophecies become a massive problem. See the next problem which feeds into the above statement.
The WTBTS's claim to be a prophet.
So, does Jehovah have a prophet to help them, to warn them of dangers and to declare things to come? These questions can be answered in the affirmative. Who is this prophet? . . . This "prophet" was not one man, but was a body of men and women. It was the small group of footstep followers of Jesus Christ, known at that time as International Bible Students. Today they are known as Jehovah's Christian witnesses . . . Of course, it is easy to say that this group acts as a "prophet" of God. It is another thing to prove it...
Watchtower, Apr. 1, 1972, p. 197.
The only way to prove the WTBTS is a prophet, is to check the record of course. Deuteronomy provides us with the criteria:
But the prophet who presumes to speak a word in my name that I have not commanded him to speak, or who speaks in the name of other gods, that same prophet shall die.’ And if you say in your heart, ‘How may we know the word that the Lord has not spoken?’— when a prophet speaks in the name of the Lord, if the word does not come to pass or come true, that is a word that the Lord has not spoken; the prophet has spoken it presumptuously. You need not be afraid of him.
Deuteronomy 18:20-22 English Standard Version (ESV)
Jehovah’s Witnesses have admitted serious errors. In their official Watchtower publication, Man’s Salvation (1975), they now admit that Charles Taze Russell (the founder) was wrong in his 1874 prediction of Christ’s second coming.  They admit that they were wrong in their 1914 prediction.  They admit that they were wrong in their prediction of 1925.  They admit that they were wrong about their prediction in 1975.
In May 1974 the Watch Tower Society told members regarding the 1975 date that:
Reports are heard of brothers selling their homes and property and planning to finish out the rest of their days in this old system in the pioneer service. Certainly this is a fine way to spend the short time remaining before the wicked world's end.
"How Are You Using Your Life?". Our Kingdom Ministry. May 1974. p. 3.
The failure of the 1975 prophecy caused the JW numbers to decline from 1976 onwards. This trend was not reversed until 1980. 
Problem 1 & 2 amounts to a devastating internal critique of the JW worldview. They cannot hold to the Bible as their ultimate authority as the Watchtower claims that reading the Bible alone leads to apostasy. Neither can the Watchtower be their authority as they have discredited themselves as a prophet by Biblical standards. So what's the JW to do? Having no authority to appeal to, the JW finds himself/herself unable to justify the preconditions of knowledge leading to an absurd worldview.
The JW confesses that God is only person within the one being that is God, compared to the Scriptural teaching that God is three persons within the one being that is God.
The first article expands greatly on this, however for this article we'd like to focus on God's love. Ask the JW whether God is love. If the answer comes in the affirmative, point out that a God who is love makes no senses without plurality in his being. God is one, however without plurality in His being, He could not be love, as prior to creating man He would have no one to love.
Ask the JW whether God can die.
The NWT claims God cannot die.
Are you not from everlasting, O Jehovah? O my God, my Holy One, you do not die. O Jehovah, you appointed them to execute judgment; My Rock, you established them for punishment.
Habakkuk 1:12, NWT
The NWT claims God (the Alpha and Omega) died.
“I am the Alpha and the Omega,” says Jehovah God, “the One who is and who was and who is coming, the Almighty.”
Revelation 1:8, NWT
When I saw him, I fell as dead at his feet. And he laid his right hand on me and said: “Do not be afraid. I am the First and the Last, and the living one, and I became dead, but look! I am living forever and ever, and I have the keys of death and of the Grave.
Revelation 1:17-18, NWT
This of course amounts to a contradiction if you deny the divinity of Christ.
Changes to Watchtower doctrine.
Regarding the 1914 date:
But bear in mind that the end of 1914 is not the date for the beginning, but for the end of the time of trouble.
After the 1914 prophecy failed to come true, they changed their stance:
Jehovah's witnesses pointed to the year 1914, decades in advance, as marking the start of the conclusion of the system of things.
Just to be sure, the Witness may tell you that 1914 was not predicted to be the end time. This is false. Their 'Studies in the Scriptures - Thy Kingdom Come' pre 1914 indicates:
That the deliverance of the saints must take place some time before 1914 is manifest...
And the post 1914 version (1923) indicates:
That the deliverance of the saints must take place very soon after 1914 is manifest...
This is about as clear a contradiction and outright change to doctrine as one can get.
Jehovah's Witnesses are not to read any material given to them by apostates.
It would be a mistake to think that you need to listen to apostates or to read their writings to refute their arguments. Their twisted, poisonous reasoning can cause spiritual harm and can contaminate your faith like rapidly spreading gangrene. (2 Timothy 2:16, 17) Rather, imitate God's response to apostates. Job said of Jehovah: "Before him no apostate will come in." - Job 13:16."
Watchtower 2004 Feb 15 p.28
There are numerous other quotations as well and can be found here.
Engaging with the idea, it seems self-contradictory. The JWs on the street always points you the JW.org website and expects us to read their material, but if we consistently apply their own standard it destroys the platform for discussion. It is also inconsistent with the method of the apostle Paul. Did Paul quote pagan unbelievers in the New Testament? Yes, he did. But, he did not quote them for the purpose of supporting them. Instead, he quoted them here and there to aid in defending and spreading the gospel. But, for him to do this, he would have had to study their teachings. If Paul could do it, so can we as long as we are putting quotes in the proper context either exposing error and or building a bridge by which we might better present the truth of God's word. Paul quoted three pagan philosophers, Epimenides, Menander and Aratus in the New Testament.
This again puts the Witness in tension between his/her two authorities which is the Bible or the Watchtower.
Contradictions amount to lying. The JW doctrine when closely analysed is littered with contradictions and inconsistencies. Contradictory and inconsistent authorities cannot act as a foundation for a person's worldview as it will reduce the entire worldview to absurdity. The JW doctrine fails to provide a foundation for knowledge and as a result should be abandoned.
The issue if course is that people will much rather choose absurdity than choose Christ. Once the worldview has been exposed it does not mean that the JW will readily embrace the true Christ. We need to preach the Gospel to them, the real Gospel. Don't assume they already know what the Gospel is. They might use the same words, however, they don't comprehend what Christ has done on the cross for His people. Preach the Gospel start to finish. You can also use on of our tracts which gives a summary of the Gospel.
Always remember to approach the witnesses with love and respect, knowing that apart from the grace of God, it might as well have been you standing on the corner preaching heretical doctrine.
Man’s Salvation Out of World Distress at Hand, op. cit., p. 312.
1975 Yearbook of Jehovah’s Witnesses (WBTS, 1974), p. 76.
Ibid., pp. 145-146.
Singelenberg, Richard (1989). "It Separated the Wheat From the Chaff: The 1975 Prophecy and its Impact Among Dutch Jehovah's Witnesses". Sociological Analysis. 50 (Spring 1989): 23–40.